Umaima is 4 times as old as Ashley and is also 15 years older than Ashley. How old is Ashley?
Solution: We can use the given information to write down two equations that describe the ages of Umaima and Ashley. Let Umaima's current age be $u$ and Ashley's current age be $a$ $u = 4a$ $u = a + 15$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $a$ , and both of our equations have $u$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $4a$ $-$ $ (a + 15)$ which combines the information about $a$ from both of our original equations. Solving for $a$ , we get: $3 a = 15$ $a = 5$.